Likelihood-based modelling of age-related normal ranges for ordinal measurements: changes in visual acuity through early childhood.

This paper investigates the construction of age-related standards for ordinal outcome data. Asymmetric logistic models are used to describe the age-related changes in the cumulative probabilities for each ordinal level. Maximum likelihood estimation of model parameters allows the use of likelihood ratio tests to ascertain the appropriate model complexity. In contrast to methodologies for constructing age-related standards where the outcome is continuous, we show how the methodology leads directly to centile estimation for individuals. The method is illustrated using visual acuity measurements collected from 2968 children between 2 and 9 years of age made on a 30-point ordinal scale. We show how, in this instance, smoothing of parameters across ordinal categories leads to reduced validity of the centiles, justifying the need for specialized methodology for non-continuous outcomes.

The maturation of linear acuity and compliance with the Sonksen-Silver Acuity System in young children.

The compliance and maturation of visual acuity of 1245 2 1/2- to nine-year-olds was investigated. Testing was undertaken as part of routine surveillance. Ability to letter match, to achieve a binocular measure and to achieve monocular measures for children under three years was 89, 78 and 37 per cent, for children aged three to four years 97, 91 and 66 per cent, and for children over four years 99.9, 99.9 and 99, respectively. A statistical model was developed to give acuity norms by age for use by surveillance and diagnostic teams.

Measures of acuity in primary-school children and their ability to detect minor errors of vision.

492 five to nine year old children participated in a study of the ability of three tests of linear acuity --the Sonksen-Silver Acuity System (SSAS), the Sheridan Gardiner 7-letter chart and the Keelers MK2 chart to identify children requiring specialist visual examination. The ability of the three tests to detect children with visual defects at 6m and of the SSAS in several test test conditions (3m and 6m, monocular and binocular) was investigated at two acuity levels for referral (3/4.5 or 6/9 and 3/6 or 6/12). Although specificity was very high for all tests and test conditions using a 3/6 or 6/12 cut-off for referral, the sensitivity and yield were disappointingly low; higher levels of the latter were achieved at the expense of a degree of specificity using a 3/4.5 or 6/9 cut off. Similarly, sensitivity and yield were greater for the monocular than binocular condition and for the 6m than 3m condition. A test of near vision (SSAS) did not detect any children not already identified by a distance measure. The optometric and developmental rationale behind the differences is discussed.

Age-related standards for ordinal data: modelling the changes in visual acuity from 2 to 9 years of age.

The visual acuities of 1140 children between the ages of 2 and 9 years were measured using the Sonksen-Silver Acuity System (SSAS) from a distance of 3 metres. Ordered logistic regression was used to construct smoothly changing age-related reference ranges for the proportions of children at different ages expected to have acuities in each of three ordinal categories. Exponential functions of age fitted the data better than polynomials. The resulting reference ranges can be used to derive the ages at which a given percentage of children achieve each of the acuity cut-offs. However, since it is unlikely that all children will be available for testing at the exact appropriate age, two possible alternatives are introduced and discussed. First, a new ordinal category that would result in a chosen outcome at a pre-selected age is calculated. Secondly, because it may be more feasible to use the current SSAS system whilst varying the distance of measurement, age-related standards showing the distances required to give constant pass-rates with the usual letter-sizes are also presented.

Patterns of visual impairment associated with lesions of the preterm infant brain.

The visual function of 42 children with haemorrhagic and/or ischaemic cerebral lesions acquired before a gestational age of 35 weeks was examined and related to cranial ultrasound in the neonatal period and to MRI and neurodevelopmental status at follow-up. All 37 children with abnormal ultrasound scans and one of the five with normal ultrasound scans showed impairment of one or more aspects of visual function. While impaired acuity was more frequent among infants with MRI evidence of visual pathway damage, this was not an invariable finding. Normal or near-normal visual acuity did not preclude the presence of other functional visual deficits. The authors conclude that preterm cerebral insults may produce a variety of visual difficulties, the pattern and severity of which cannot be predicted on imaging. Each child therefore requires individual assessment of multiple aspects of visual function.

Developmental setback in severe visual impairment.

Developmental setback in children initially thought to be of normal cognitive potential is a serious complication of severe visual impairment; the prevalence, diagnostic specificity, clinical presentation, and factors that contribute to its genesis require systematic investigation. The findings are reported of a retrospective case review over a 15 year period of children attending the developmental vision clinic at the Wolfson Centre of the Institute of Child Health. One hundred and two children met the inclusion criteria of a period of normal development confirmed at initial assessment when aged less than 16 months, absence of additional disabilities, and follow up to at least 2.5 years of age. Developmental setback in their second or third year occurred in 10 (31%) of 32 children who were totally blind throughout (minimal perception of light or less), one (4%) of 25 who, though blind at first assessment, showed visual improvement, and none of 49 children with better vision throughout (awareness for near, large objects). This represents a significantly greater risk for totally blind children than for the other groups. The course and characteristics of the affected children varied, but all had visual diagnoses involving the nervous elements of the visual system, and 60% had major social adversity factors. The role of primary maldevelopment of the central nervous system, the degree of visual impairment, the developmental and emotional climate, and the stage of attentional and behavioural development in the causation of adverse developmental outcome are discussed.

Evaluation of the Sonksen picture test for detection of minor visual problems in the surveillance of preschool children.

The Sonksen Picture Test (SPT) for surveillance of vision in preschool children was evaluated in 842 children, aged 21 to 60 months, from nine health districts in England, Wales and Scotland. The failures and controls were refracted and examined for squint; the Sheridan-Gardiner seven-letter chart (SGLC) was also used with children of > or = 42 months. The SPT was quicker to administer than the SGLC, with median times of one and five minutes, respectively. 98 per cent of children of all ages completed the SPT, whereas 10 per cent of those over 42 months were unable to complete the SGLC. The test method that has been established is developmentally appropriate for this age-group, more so than optotype tests. It is a binocular test that is quick, cheap and simple to administer, and is available to children under five years.

Congenital retinal dystrophies: a study of early cognitive and visual development.

The reported incidence of mental retardation in Leber's congenital amaurosis has varied from 10% to 87%. There has been no review of the estimate since it became possible to delineate an increasing number of diagnostic subcategories. In this study, the visual and cognitive development of 38 children with congenital retinal dystrophies has been followed up prospectively. Children with associated disorders in other systems and those with central nervous system malformations or degenerations were significantly more likely to have learning disability than those without additional medical problems. Most subgroups made little or no visual progress with the exception of the group with associated hypoplasia of the cerebellar vermis. The study highlights the importance of using the specialised techniques now available to delineate fully the visual diagnosis and paediatric perspective because of their relevance to cognitive and visual prognosis.

Promotion of visual development of severely visually impaired babies: evaluation of a developmentally based programme.

A developmentally based programme (PVD) to promote the visual development of babies with severe visual impairment was evaluated in 58 infants aged between one month and 13 months of age. Progress in nine aspects of visual development was significantly greater for babies receiving the programme. This benefit extended to those with severe learning disability, or with minimal or apparently no vision at entry. The PVD favourably influenced visual outcome when introduced at any time during the first 13 months of life, although earlier introduction enabled greater benefit to be derived from the improved vision. Therefore, it is recommended that infants are referred to a developmental centre as soon as severe visual impairment is suspected.

Norrie's disease: a prospective study of development.

Developmental progress, hearing, and dysmorphic features were monitored prospectively in eight babies with Norrie's disease (an X linked form of congenital blindness believed to be associated with mental retardation, regression, sensorineural deafness, and dysmorphic features) and in six congenitally blind peers during their preschool years. No evidence of sensorineural deafness or dysmorphology was found in the group with Norrie's disease. No significant difference in the rate of developmental progress occurred between the two groups. All 14 children showed continuing developmental progress and in 10 this was at a normal or superior rate. Two cases and two controls showed slowing in their rate of progress; in both groups a suboptimal developmental climate had prevailed and may have been contributory. The emphasis on serious and progressive associated disabilities in past reports has led to considerable distress for families of children with this disease. Our study suggests that these anxieties may often be illfounded. Parental depression constrains development, particularly when a baby is blind. More optimistic counselling with developmental guidance is recommended for children who are not overtly retarded in infancy until the long term developmental perspective of this disease is further clarified.

Low vision aids for preschool children.

A study was made of the use of low vision aids to augment the vision of children with very severe visual disability. This paper reports the results for 28 children, using a 'lobster pot' stand magnifier, 26 of whom were aged between 18 and 60 months. Success was evaluated by measuring functional vision for nursery-age learning material in aided and unaided conditions. Half the children showed improved functional vision and one-third retained the magnifier for continued use. The influence of visual power and developmental maturity in five key areas was explored. A two-year developmental level was shown to be adequate, with some interaction between developmental maturity and visual level. There was also a tendency for unaided functional vision to improve during the trial period with the magnifier at home.

Vision for coloured pictures at different acuities: the Sonksen picture guide to visual function.

The vision 70 normal-sighted children was tested for both Snellen letters and life-size colour pictures of everyday objects. All the children wore spectacles for the tests: 60 were fitted with lenses which would induce a refractive error, the remainder had glassless frames only. Compared with acuity measures based on the Snellen letters, the pictures needed to be brought much closer than might be expected before the children with induced minor visual errors could recognise them. This highlights the importance of detecting and correcting refractive errors in preschool children who learn from such material, and suggests that the pictures may be a useful tool for detecting children with such errors. 18 pictures, comprising the Sonksen Picture Guide to Visual Function, have now been selected for this purpose.

A developmental approach to sensory disabilities in early childhood.

Rehabilitation for young children with hearing and visual disabilities is considered from a developmental angle. The effect of these sensory disabilities on parents; the constraints on development imposed by each disability; and medical and surgical treatment and the use of aids in young children are discussed.

Identification of constraints acting on motor development in young visually disabled children and principles of remediation.

Babies and preschool children with severe visual disabilities have been studied in a developmentally orientated clinical research setting. Severe congenital visual disability delays and alters development in all areas; the impact on motor development is complex with much secondary to delays in other areas. The constraints on motor development are identified and discussed together with ideas for remediation and developmental prevention.

The assessment of 'vision for development' in severely visually handicapped babies.

Vision makes a substantial contribution to the pattern and rate of normal development. Considering infant development in 3 phases, global, integrative and specific the most important attributes to vision of development within each phase are discussed. A method for assessment of the aspects of vision most relevant to each child's current developmental needs is described and a philosophy outlined whereby the findings can be represented as a balanced practical prescription for development. The development of the visual system is often delayed in visually handicapped babies; some reasons are put forward and a concern that many may never achieve their potential maximum visual competence is expressed. A method for evaluating the current stage of visual development in a visually handicapped baby is described in which the findings form the starting point of a programme towards achieving maximum visual competence as young as possible.

Sound and the visually handicapped baby.

The part played by vision in learning to interpret both speech and environmental sounds and to localize the latter is discussed in the light of observations of the development of sighted and of blind babies. Subsequently, some suggestions of guidance strategies based on these observations, are put forward to help visually handicapped babies acquire localization skills. Preliminary experience using these techniques has been promising and they are being further developed and researched at The Wolfson Centre in London.

The assessment needs of pre-school children with handicaps of language development.

An outline of the paediatric assessment needs of children with delayed or deviant language development has been given based on the experience and findings of the research language team at the Wolfson Centre.